Plasma processing apparatus

ABSTRACT

A plasma processing apparatus including: a monitor device which monitors a process quantity generated at plasma processing; a monitor value estimation unit which has monitor quantity variation models for storing change of a monitor value of the process quantity in accordance with the number of processed specimens and which estimates a monitor value for a process of a next specimen by referring to the monitor quantity variation models; and a control quantity calculation unit which stores a relation between a control quantity for controlling the process quantity of the vacuum processing device and a monitor value and which calculates the control quantity based on a deviation of the estimated monitor value from a target value to thereby control the process quantity for the process of the next specimen. Thus, a process model indicating variation of the state of a process processing apparatus can be added to a control loop in such run-to-run control that process conditions are changed according to each wafer process, so that stable processed results can be obtained even when variation occurs in processes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasma processing apparatus.Particularly, it relates to a plasma processing apparatus which cansuppress an influence caused by change of a process condition occurringwith the progress of plasma processing.

2. Description of the Background Art

For example, the plasma processing apparatus is an apparatus forimporting an etching gas into a vacuum process chamber, generatingplasma discharge in the imported etching gas under a reduced pressure tothereby generate radicals or ions, and inducing the radicals or ions toa surface of a wafer as a subject of processing to make the radicals orions react with the surface of the wafer to thereby etch the surface ofthe wafer.

With the advance of reduction in size of a produced device, such aplasma processing apparatus might not be able to obtain desiredperformance because of various disturbances even when a predeterminedrecipe was used for processing.

Therefore, run-to-run control capable of suppressing an influence causedby various disturbances has been used. Run-to-run control is a techniquefor changing a recipe as a production condition in accordance with eachwafer or lot to be processed so that an influence caused by change ofprocess conditions can be suppressed.

For example, JP-A-2003-17471 has disclosed a plasma processing apparatusfor processing a specimen contained in a vacuum process chamber, whichincludes a sensor for monitoring a process quantity during processing, aprocessed result estimation model for estimating a processed result, andan optimum recipe calculation model for calculating an optimum recipebased on the result estimated by the processed result estimation model,wherein plasma processing is controlled based on the recipe generated bythe optimum recipe calculation model.

On the other hand, JP-A-2006-72791 has disclosed a model predictivecontrol apparatus for predicting a subject of control by using controlsubject models and evaluating the prediction to perform optimum controlon the subject of control, which includes control subject models withdifferent sampling periods, wherein one of the control subject models isselected in accordance with change of the sampling period so that bothshortening of arithmetic processing time and securement of predictionaccuracy can be achieved.

In a plasma etching apparatus, an etching process is generally performedbased on a predetermined process condition called recipe. Etchingperformance (etching rate, etching size, etc.) however often varies inaccordance with change of the state of a reaction product deposited onan inner wall or the like of a process chamber, the wear-out degree ofeach component, etc. To reduce such variations, run-to-run control forchanging the process condition in accordance with each wafer to beprocessed may be used as described above.

Etching rate and processing size are indices for judging whether theresult processed by the etching apparatus is good or not. It is howevernecessary to convey the wafer to an inspection device for measuring theetching rate or processing size. For this reason, a unit capable ofevaluating the processed result (performance result) immediately afterprocessing is required for achieving run-to-run control in accordancewith each wafer to be processed.

Assume now that the performance result is not directly measured butindirectly measured based on data which can be monitored duringprocessing such as plasma light emission. When, for example, therelation between a monitor value and a performance result is formed as amodel in advance, the model can be referred to so that the monitor valuecan be used in place of the performance result.

Incidentally, for achievement of such run-to-run control, it isnecessary to generate a control model by modeling the relation between aprocess monitor value clearly associated with a processed resultobtained in accordance with each wafer to be processed and a controlvariable capable of controlling the process monitor value.

FIG. 2 is a graph of a control model generated by modeling the relationbetween a monitor value of plasma light emission during an etchingprocess and a gas flow rate as a process condition. This model shows therelation between the flow rate of an oxygen gas as a gas imported duringthe etching process and the light emission intensity of a wavelengthindicating oxygen as the monitor value of plasma light emissionintensity obtained during the process.

In FIG. 2, the reference numeral 1 designates a value which indicatesplasma light emission intensity when the process (etching process) isexecuted without any trouble and which is a target value for run-to-runcontrol. That is, when plasma light emission intensity takes the targetvalue 1, for example, the processing size as an etching performanceresult is a desired size.

On the other hand, when plasma light emission during the process takes alarger value or a smaller value than the target value 1, the etchingperformance result is not a desired value because the value of plasmalight emission indicates some change of the process condition.

Run-to-run control operates to bring the performance result close to atarget value when the performance result is likely to go out of thedesired value. That is, in run-to-run control, control quantity for anext process (e.g. next wafer process) is calculated based on adifference between the obtained process monitor value and the targetvalue 1 and a process condition (recipe) for the next process iscorrected based on the calculated control quantity so that the processis executed in the corrected process condition.

FIG. 3 is a graph showing plasma light emission intensity obtained byexecution of run-to-run control using the aforementioned control modelwhen values of the plasma light emission intensity are plotted inaccordance with wafer processes. In FIG. 3, the reference numeral 2designates a time point that a product lot to be processed is changed.

In this example, plasma light emission intensity is designed to convergeat the target value 1 by run-to-run control. There may be however thecase where it impossible to perform control to make the plasma lightemission intensity coincident with the target value 1. In practice, theplasma light emission intensity is controlled with some variation 3 asshown in the example of FIG. 3. Because this variation means that theperformance result varies, this variation exerts an influence onperformance of produced products. Such a variation is caused by the factthat the control model cannot reflect all process conditions occurringin the process chamber.

Incidentally, the example disclosed in JP-A-2003-17471 cannot be appliedto such a long-term process change that the process condition changes ina lot or between lots. In addition, in the example disclosed inJP-A-2006-72791, the control subject models with different samplingperiods cannot be applied to such a process that the process conditionchanges in accordance with each term (in a lot or between lots).

The invention is accomplished in consideration of the aforementionedproblems. An object of the invention is to provide a plasma processingapparatus which can execute run-to-run control in which the processcondition of the apparatus is reflected, and which can obtain stableperformance results.

SUMMARY OF THE INVENTION

To solve the aforementioned problems, the invention uses the followingmeans.

A plasma processing apparatus for generating plasma in a vacuumprocessing device and applying plasma processing to specimens disposedin the vacuum processing device by use of the generated plasma,including: a monitor device which monitors a process quantity generatedat plasma processing; a monitor value estimation unit which has at leastone monitor quantity variation model for storing change of a monitorvalue of the process quantity in accordance with the number of processedspecimens and which estimates a monitor value for a next process byreferring to the monitor quantity variation model; and a controlquantity calculation unit which stores a control model indicating arelation between a control quantity for controlling the process quantityof the vacuum processing device and a monitor value and which calculatesthe control quantity based on a deviation of the estimated monitor valuefor the next process from a target value to thereby control the processquantity.

With the aforementioned configuration, the invention can provide aplasma processing apparatus which can execute run-to-run control inwhich the process condition of the apparatus is reflected, and which canobtain stable performance results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a plasma processing apparatusaccording to an embodiment of the invention;

FIG. 2 is a graph of a control model generated by modeling the relationbetween plasma light emission and a gas flow rate as a processcondition;

FIG. 3 is a graph showing plasma light emission intensity at run-to-runcontrol;

FIG. 4 is a graph showing a trend of plasma light emission intensitywithout execution of run-to-run control;

FIG. 5 is a view for explaining an example of a process model obtainedby combining a long-term variation model, a short-term variation modeland a control model;

FIG. 6 is a graph for explaining a method of calculating a controlquantity for a next process;

FIG. 7 is a flow chart showing a control flow of run-to-run control;

FIG. 8 is a graph for explaining a method of moving a variation model;

FIG. 9 is a graph for explaining a method of generating a movedshort-term variation model;

FIG. 10 is a series of graphs for explaining a method of calculating anestimated monitor value for a next process based on the long-termvariation model and the short-term variation model;

FIGS. 11A and 11B are views for explaining forms of run-to-run control;

FIGS. 12A to 12D are views showing examples as to how the form of acontrol method changes in accordance with a subject of monitor and asubject of control when run-to-run control is executed; and

FIG. 13 is a view showing an example of a control form in the case wherechange of a lot exists in the control form shown in each of FIGS. 12A to12D.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will be described below with reference tothe accompanying drawings. Although an aim in modeling processconditions will be described first while a plasma etching apparatus istaken as an example, the invention can be applied to any processingapparatus using plasma, such as a plasma CVD apparatus.

FIG. 4 is a graph showing an example of observation of a trend of plasmalight emission intensity without execution of run-to-run control. InFIG. 4, the horizontal axis shows the number of processed wafers, andthe vertical axis shows a plasma light emission monitor value. In FIG.4, each separating line 2 shows change of a product lot to be processed.Incidentally, the plasma light emission monitor value is an indicatorfor indicating etching performance.

Referring to FIG. 4, it is found that there are a pattern 10 in whichthe monitor value increases in accordance with the change of each lot,and a pattern 11 in which the monitor value decreases totally.

First, the increasing pattern 10 is repeated in accordance with eachseparating line 2. Although the separating line 2 is a line indicatingchange of a lot, the separating line 2 is a unit for performing trialrunning of a process chamber called aging or plasma cleaning forcleaning the chamber with plasma in terms of process.

That is, when a wafer process is repeated, the internal state of thechamber such as the state or temperature of an inner wall of the chambervaries according to each process, so that a process environment changes.The change of the environment results in change of plasma light emissionintensity. When aging or plasma cleaning is executed, the state of theprocess chamber is restored to a state close to the initial state andthe chamber environment is reflected on plasma light emission intensityso that the plasma light emission intensity is restored to a state closeto the initial state.

By repeating this, each pattern 10 of plasma light emission intensityappears.

There is however the case where the state of the chamber cannot berestored to the original state perfectly by aging or plasma cleaningexecuted in accordance with each lot. Deviations from the original stateare exhibited in the pattern 11.

The state of the chamber can be however restored to the initial statewhen cleaning of the process chamber opened to the atmospheric air,called wet cleaning, is executed. That is, the pattern 11 is repeated inaccordance with the wet cleaning.

Although the shapes of patterns are shown here as an example, patternsmay have various forms in accordance with the subject of processing, theprocess condition, the apparatus, etc. That is, the patterns can bereworded as process models. Accordingly, one of the patterns 10 and 11is referred to as “short-term variation model” because the pattern 10appears in a relatively short term, while the other pattern 11 isreferred to as “long-term variation model” because the pattern 11appears in a relatively long term.

Incidentally, consideration of only the short-term model orconsideration of only the long-term model may be required in accordancewith the process.

In the background art, only one control model indicating the relationbetween a process monitor value and a control variable was applied to acontrol loop to execute run-to-run control. Some process condition washowever impossible to express only in the control model. As a result,the control varied. It is therefore apparent that more stable controlthan the control according to the background art can be achieved ifcontrol is executed while the aforementioned long-term and short-termvariation models are considered in addition to the control model.

FIG. 5 is a view for explaining an example of a process model obtainedby combining a long-term variation model, a short-term variation modeland a control model.

The process model indicating the process behavior of the inside of aprocess chamber 100 at the time of execution of run-to-run control is amodel obtained by combining a long-term variation model 21, a short-termvariation model 22 and a control model 23.

The long-term variation model 21 receives as an input a number 24 (N₁)of processed wafers from wet cleaning and outputs a plasma lightemission monitor value 18. For example, the long-term variation model 21can be given as a model represented by the expression 1:Y ₁ =A ₁ ×B ₁ ^((N) ¹ ^(+C) ¹ ⁾ +D ₁  (1)in which Y₁ is the process monitor value (e.g. plasma light emissionmonitor value), N₁ is the number of processed wafers from wet cleaning,and A₁, B₁, C₁ and D₁ are long-term variation model coefficients.

Although description has been made here in the case where N₁ is thenumber of processed wafers from wet cleaning, a process for resettingthe long-term variation model may be provided so as to be regarded as astarting point so that N₁ is the number of processed wafers from theresetting process.

The short-term variation model 22 receives as an input a number 25 (N₂)of processed wafers in a lot and outputs a plasma light emission monitorvalue 19. For example, the short-term variation model 22 can be given asa model represented by the expression 2:Y ₂ =A ₂ ×N ₂ ² +B ₂ ×N ₂ +C ₂  (2)in which Y₂ is the process monitor value (e.g. plasma light emissionmonitor value), N₂ is the number of processed wafers in a lot, and A₂,B₂ and C₂ are short-term variation model coefficients.

The control model 23 receives as an input a gas change quantity 26 (X₃)and outputs a plasma light emission monitor value 20. For example, thecontrol model 23 can be given as a model represented by the expression3:Y ₃ =A ₃ ×X ₃  (3)in which Y₃ is the process monitor value (e.g. plasma light emissionmonitor value), X₃ is a control quantity, and A₃ is a control modelcoefficient.

An output 103 of the process chamber 100 is expressed as a combinationof the outputs 18, 19 and 20 of the respective models.

As described above, because the internal state of the process chambercan be expressed by a combination of the models, an apparatus capable ofcontrolling a process stably can be achieved if a control system isconstructed in accordance with the combination of the models.

FIG. 1 is a diagram showing a plasma processing apparatus according toan embodiment of the invention in the case where a plasma etchingapparatus is used as an example of the plasma processing apparatus.

A wafer 117 as a subject of an etching process is conveyed to theprocess chamber 100 and subjected to a plasma etching process. Theetching process is executed while an apparatus controller 114 controlsan actuator 101 in accordance with a production condition called recipe.The actuator 101 controls a power supply, a pressure control device, amass-flow controller, etc.

A process monitor 102 monitors the state of the process chamber 100during the etching process. For example, an emission spectrometer forspectroscopically monitoring plasma light emission during the etchingprocess is used as the process monitor 102.

A monitor value estimation unit 104 has a long-term variation modeldatabase 109 and a short-term variation model database 110. Variationmodels to be processed by the apparatus are stored in the databasesrespectively in accordance with each recipe or each recipe group.Incidentally, each recipe group is a set of recipes to which one and thesame variation model can be applied. Further, past information of wafersprocessed in the process chamber 100, such as the number 24 of processedwafers from wet cleaning, the number 25 of processed wafers from the topof each lot, etc. can be acquired from a process history managementportion 116. Incidentally, the number 25 of processed wafers from thetap of each lot is provided as the number of wafers processed in eachprocess chamber. When, for example, a lot of 25 product wafers areprocessed separately in two process chambers, 13 wafers ford one lot inone process chamber and 12 wafers form one lot in the other processchamber in terms of the number 25 of processed wafers.

The monitor value estimation unit 104 calculates an estimated monitorvalue 105 for a next process without execution of run-to-run control, byusing these pieces of information and the measured monitor value 103.

The estimated monitor value 105 for the next process without executionof run-to-run control, which value is calculated by the monitor valueestimation unit 104, is compared with a target value 106 of the processmonitor value, so that a deviation 112 of the estimated monitor value105 from the target value 106 is calculated. Incidentally, the targetvalue 106 is a value which has been set in advance in accordance witheach recipe or each recipe group.

A control quantity calculation unit 111 has a control model database115. Control models to be processed by the apparatus are stored in thedatabase 115 in accordance with recipes or recipe groups. The controlquantity calculation unit 111 calculates a control quantity 107 for anext process based on a control model selected from the control modeldatabase 115 and the deviation 112.

FIG. 6 is a graph for explaining a method of calculating the controlquantity for the next process. When a point at which the calculateddeviation 112 is drawn on the control model 23 can be found in FIG. 6,the control quantity 107 for the next process can be calculated.Incidentally, the control quantity 107 is a value indicating a changequantity with respect to each recipe. In run-to-run control according tothe invention, the process is executed while a part of conditionsconstituting the recipe are changed based on the calculated deviation112 but the other part of the conditions are left untouched as shown inthe recipe.

The apparatus controller 114 shown in FIG. 1 has recipes 113 which areprocess conditions in accordance with products or product groups to beprocessed in the process chamber 100. The apparatus controller 114controls actuators 101 of the apparatus in accordance with the recipes113 to execute processes in accordance with the process conditionsrespectively. When each process is executed, the process history isupdated.

On this occasion, each control target item of a recipe 108 is increasedor decreased by the next process control quantity 107 calculated by thecontrol quantity calculation unit 111. One recipe is generally composedof a plurality of items but a part of the items are changed based on thecontrol quantity 107.

The plasma processing apparatus according to this embodiment repeats theaforementioned processing in accordance with each wafer process.

Incidentally, run-to-run control can be applied not only to a recipe forproduct wafers but also to a recipe for a plasma cleaning processexecuted between product wafer processes. For example, the invention canbe applied to run-to-run control for such cleaning processes that arecipe for a current cleaning process is changed to another recipe for anext cleaning process. The invention can be further applied to suchrun-to-run control that a result (monitor value) of each cleaningprocess is reflected on a product process or vice versa.

FIG. 7 is a flow chart showing a control flow of run-to-run control. Acontrol flow start point 601 is just before start of a product processafter completion of wet cleaning of the process chamber.

In step 602, determination is made as to whether the process is asubject of run-to-run control or not. For example, a process calledaging may be applied at the top of each lot and a cleaning process maybe applied between product wafers when a product lot (of 25 productwafers) is to be processed. If only product wafers are intended forrun-to-run control in this case, aging and cleaning are not intended forrun-to-run control. Incidentally, the cleaning process may be intendedfor run-to-run control.

In step 603, a process monitor value obtained during the process isacquired. The acquired monitor value is the latest value processed inthe past based on the same recipe or recipe group as in the nextprocess. On this occasion, the monitor value may be calculated byaveraging or statistical processing in accordance with each processprocessing time or each step or may be calculated by multivariateanalysis such as principal component analysis.

In step 604, an uncontrolled monitor value is calculated based on theacquired monitor value. As for a calculation method, a control quantityon the occasion that the acquired monitor value was processed and acontrol model used on this occasion are used for calculating back to amonitor quantity (deviation) changed by control. Then, a differencebetween the acquired monitor value and the calculated-back monitorquantity (deviation) is calculated as an uncontrolled monitor value.

In step 605, determination is made as to whether a long-term variationmodel to be used for later calculation needs to be moved or not, orwhether a short-term variation model to be used for later calculationneeds to be moved or not. For example, a long-term variation model ismoved for processing of the first wafer in a product lot or processingjust after aging, but a short-term variation model is moved forprocessing of the second wafer or each wafer after the second wafer inthe product lot or processing just after plasma cleaning betweenproducts. In step 606 or 607, the long-term variation model or theshort-term variation model is moved.

FIG. 8 is a graph for explaining a method of moving a variation model(short-term variation model).

First, when the uncontrolled monitor value obtained in the step 604 isplotted, a point 31 is obtained as shown in FIG. 8. As for a modelmoving method, a short-term variation model 32 before movement is movedin parallel so as to be put on the uncontrolled monitor value 31 tothereby form a moved short-term variation model 33. For example, theshort-term variation model represented by the expression 2 can be movedin parallel when the value of C₂ is changed so that the moved short-termvariation model passes through the uncontrolled monitor value 31.

Alternatively, as shown in FIG. 9, the coefficients A₂ and B₂ in theexpression 2 may be changed to generate a moved short-term variationmodel 35. A method according to process variation as a subject ofcontrol can be selected as the model moving method. Although the methodof moving a short-term variation model has been described here, themethod of moving a long-term variation model can be performed in thesame manner as described above.

In step 608, an estimated monitor value for a next process iscalculated. This value is a value estimated based on the long-termvariation model and the short-term variation model when control is notperformed (the recipe is not changed) in the next process.

FIG. 10 is a series of graphs for explaining a method of calculating anestimated monitor value for a next process based on the long-termvariation model and the short-term variation model.

First, a composite model 37 is obtained based on the short-termvariation model 33 and the long-term variation model 36. The short-termvariation model and the long-term variation model used on this occasionare models moved in the steps 606 and 607. Then, a value 38 according tothe number N of processed wafers in the next process is calculated onthe composite model 37. This value 38 is used as an estimated monitorvalue for the next process.

In step 609, a deviation of the estimated monitor value calculated inthe step 608 from a target value set in accordance with each recipe oreach recipe group is calculated. That is, control will be made in thenext process so that the deviation can be adjusted in accordance withthe target value.

In step 610, a control quantity is calculated based on the deviationcalculated in the step 609 and the control model. A method ofcalculating the control quantity will be described with reference toFIG. 6. The control model 23 is a function expressing the relationbetween the control quantity and the monitor value. The control quantityis a value of increment or decrement relative to the recipe. The monitorvalue is a quantity of change of a monitor value when the recipe ischanged by the control quantity. Accordingly, the monitor value can becontrolled by the deviation from the target value when a controlquantity 107 according to the deviation 112 is calculated on the controlmodel 23. That is, the control quantity 107 is used as a controlquantity for the next process. On this occasion, the control quantity isa quantity by which the value of at least one item in process conditionsin the recipe is changed with use of a predetermined value as areference value. The process conditions in the recipe are flow rateaccording to each kind of gas, electric power, pressure, etc.

In step 611, the control quantity calculated in the previous step isadded to the recipe for the next process to thereby generate processconditions used in the next process.

In step 612, the process is executed based on the recipe to which thecontrol quantity has been added in the step 611.

In step 613, a process history for the process in the step 612indicating the number of processed wafers from wet cleaning executed onthe process chamber opened to the atmospheric air, the number ofprocessed wafers from an aging process executed at the top of each lot,etc. is recorded.

In step 614 or 616, determination is made as to whether the variationmodel is to be reset or not, after determination in the step 602 resultsin that the process is not a subject of control. For example, in thecase of the long-term variation model, the model is reset when theprocess chamber is just after execution of wet cleaning (step 615). Onthe other hand, in the case of the short-term variation model, the modelis reset just after separation of a product lot, that is, execution ofan aging process (step 617).

Each model is reset is as follows. In the example of the long-termvariation model represented by the expression 1, the variable N₁ isreset to 1 (or 0). In the example of the short-term variation modelrepresented by the expression 2, the variable N₂ is reset to 1 (or 0).Incidentally, the condition for resetting each model can be set in anyother event than the aforementioned events and there may be the casewhere each model is not reset in some event.

Although the flow shown in FIG. 7 has been described in the case whereproducts in the same recipe or the same recipe group are processedrepeatedly, the flow may be adapted, for example, to processing of kindsof products in such a manner that the method of moving the long-termvariation model or the short-term variation model is adjusted inaccordance with each product kind.

Although the flow shown in FIG. 7 has been described in the case whereonly the latest value in the past is acquired as the monitor value, itmay be conceived that past monitor values are acquired and the long-termvariation model or the short-term variation model is updated inaccordance with the tendency of change of the monitor values.

FIGS. 11A and 11B are views for explaining the form of run-to-runcontrol. Description will be made while a plasma etching apparatus istaken as an example.

An etching process in semiconductor production generally has processunits called steps. Process conditions such as gas flow rate, pressure,electric power, etc. are defined in accordance with the process unitsrespectively. One recipe is composed of a set of the conditionsaccording to the steps.

FIG. 11A shows an example of run-to-run control in the case where onestep is monitored.

As shown in FIG. 11A, plasma light emission 150 during processing instep 2 of a process N is measured by a spectroscope 151. For example,statistical processing is applied to the measured data to form a processmonitor value 152. The reference numeral 153 designates a combination ofthe monitor value estimation unit 104 and the control quantitycalculation unit 111 shown in FIG. 1. The control quantity calculated bythe unit combination 153 is allocated to corresponding recipe items ofsteps 2 and 3 as subjects of control. The control quantity may beallocated equally or may be multiplied by specific coefficients so as toincrease or decrease.

FIG. 11B shows an example of run-to-run control in the case where aplurality of steps are monitored.

Plasma light emission 170 during processing in step 2 of a process N ismeasured by a spectroscope 171. For example, statistical processing isapplied to the measured data to form a process monitor value 172. Thereference numeral 173 designates a combination of the monitor valueestimation unit 104 and the control quantity calculation unit 111 shownin FIG. 1. The control quantity calculated by the unit combination 173is allocated to corresponding recipe items of steps 2 and 3 as subjectsof control. The control quantity may be allocated equally or may bemultiplied by specific coefficients so as to increase or decrease.

Plasma light emission 176 during processing in step 4 of the process Nis further measured by a spectroscope 171. For example, statisticalprocessing is applied to the measured data to form a process monitorvalue 177. The reference numeral 178 designates a combination of themonitor value estimation unit 104 and the control quantity calculationunit 111 shown in FIG. 1. The control quantity calculated by the unitcombination 178 is allocated to corresponding recipe items of steps 4and 5 as subjects of control. The control quantity may be allocatedequally or may be multiplied by specific coefficients so as to increaseor decrease.

As described above, control logics each for monitoring one step can becombined for monitoring a plurality of steps.

FIGS. 12A to 12D are views showing examples as to how the form of acontrol method changes in accordance with a subject of monitor and asubject of control when run-to-run control is executed.

In FIGS. 12A to 12D, “Aging” designates an aging process performed atthe time of start of a lot, “CL” designates a plasma cleaning processperformed before a product process, “Product” designates the productprocess, and the arrangement thereof designates a processing sequence.

FIG. 12A shows a control form in the case where both a subject ofmonitor and a subject of control are product processes. In FIG. 12A, thereference numeral 200 means that a monitored result of a product processis used for controlling a next product process. Incidentally, a cleaningprocess (CL in FIG. 12A) may be provided between product processes asshown in FIG. 12A but control of only product processes is executed evenin this case.

FIG. 12B shows a control form in the case where both a subject ofmonitor and a subject of control are cleaning processes (CL in FIG.12B). In FIG. 12B, the reference numeral 210 means that a monitoredresult of a cleaning process is used for controlling a next cleaningprocess.

FIG. 12C shows a control form in the case where a subject of monitor isa cleaning process and a subject of control is a product process. InFIG. 12C, the reference numeral 220 means that a monitored result of acleaning process is used for controlling a next product process.

FIG. 12D shows a control form in the case where a subject of monitor isa product process and a subject of control is a cleaning process. InFIG. 12D, the reference numeral 230 means that a monitored result of aproduct process is used for controlling a next cleaning process.

FIG. 13 is a view showing an example of a control form in the case wherechange of a lot, that is, a short-term variation model exists in thecontrol form described with reference to each of FIGS. 12A to 12D. FIG.13 shows the case where run-to-run control is executed in the conditionthat both a subject of monitor and a subject of control are productprocesses like FIG. 12A. A short-term variation model is reset at changeof a lot to thereby exhibit short-term variation in the lot. In FIG. 13,the reference numeral 204 designates a time for resetting the model. InFIG. 13, the reset 204 is synchronized with an aging process executed atthe top of each lot. When there is an event of the reset 204, amonitored result of a product process (205 in FIG. 13) just before thereset is not used but a monitored result (201 in FIG. 13) of a productprocess just after the reset in the previous lot, a monitored result(202 in FIG. 13) of an aging process (Aging in FIG. 13) or a monitoredresult (203 in FIG. 13) of a cleaning process (CL in FIG. 13) betweenproduct processes is used for controlling a next product process.Incidentally, this resetting method can be applied to the other controlforms shown in FIGS. 12B to 12D.

As described above, in accordance with this embodiment, in suchrun-to-run control that process conditions are changed according to eachwafer process, a process model indicating long-term or short-termvariation of the state of a process processing apparatus is applied to acontrol loop, so that a stable processed result can be obtained evenwhen process variation such as variation in a lot or variation betweenlots exists.

What is claimed is:
 1. A plasma processing apparatus for applying plasmaprocessing by run-to-run control to specimens that are disposed in avacuum processing chamber by using plasma generated in the vacuumprocessing chamber, comprising: a first database that stores a firstmonitor value variation model indicating a correlation between a numberof specimens processed during a period from execution of wet cleaning toexecution of a next process and a monitor value of a process quantityobtained when specimens of this number have been processed; a seconddatabase that stores a second monitor value variation model indicating acorrelation between a number of specimens processed during a period fromstart of a lot process to end of the lot process and a monitor value ofa process quantity obtained when specimens of this number have beenprocessed; a process history management unit that stores the number ofspecimens processed from execution of wet cleaning to execution of anext process and the number of specimens processed from start of a lotprocess to end of the lot process; a monitor value estimation unitconfigured to obtain a composite model of the first monitor valuevariation model and the second monitor value variation model andconfigured to calculate a monitor value for a next process based on thecomposite model; a third database that stores a control model indicatinga correlation between a control quantity for controlling a processquantity of the vacuum processing chamber and a quantity of change of amonitor value; and a control quantity calculation unit configured tocalculate a control quantity for the next process which corresponds to adeviation of the monitor value calculated by the monitor valueestimation unit and a target value based on the control model; whereinthe monitor value estimation unit comprises a monitor value variationmodel movement unit configured to move the first monitor value variationmodel for processing just after aging; wherein the first monitor valuevariation model is a function of processed wafers from wet cleaning, andat least one long term variation model coefficient; wherein the secondmonitor variation model is a function of the number of processed wafersin a lot and at least one short-term model coefficient.
 2. The plasmaprocessing apparatus according to claim 1, wherein the first monitorquantity variation model is reset whenever wet cleaning is performed. 3.The plasma processing apparatus according to claim 1, wherein the nextprocess is a same product process or cleaning process as a currentprocess.
 4. The plasma processing apparatus according to claim 1,wherein a current process is a product process and the next process is acleaning process.
 5. The plasma processing apparatus according to claim1, wherein a current process is a cleaning process and the next processis a product process.
 6. The plasma processing apparatus according toclaim 1, wherein the first monitor quantity variation model isrepresented by the expression:Y ₁ =A ₁ ×B ₁ ^((N) ¹ ^(+C) ¹ ⁾ +D ₁ in which Y₁ is a process monitorvalue, which is a plasma light emission monitor value, N₁ is a number ofprocessed wafers from wet cleaning, and A₁ , B₁, C₁ and D₁ are long-termvariation model coefficients.
 7. The plasma processing apparatusaccording to claim 1, wherein the second monitor quantity variationmodel is represented by the expression:Y ₂ =A ₂ ×N ₂ ² +B ₂ ×N ₂ +C ₂ in which Y₂ is a process monitor value,which is a plasma light emission monitor value, N₂ is a number ofprocessed wafers in a lot, and A₂, B₂ and C₂ are short-term variationmodel coefficients.
 8. A plasma processing apparatus for applying plasmaprocessing by run-to-run control to specimens that are disposed in avacuum processing chamber by using plasma generated in the vacuumprocessing chamber, comprising: a first database that stores a firstmonitor value variation model indicating a correlation between a numberof specimens processed during a period from execution of wet cleaning toexecution of a next process and a monitor value of a process quantityobtained when specimens of this number have been processed; a seconddatabase that stores a second monitor value variation model indicating acorrelation between a number of specimens processed during a period fromstart of a lot process to end of the lot process and a monitor value ofa process quantity obtained when specimens of this number have beenprocessed; a process history management unit that stores the number ofspecimens processed from execution of wet cleaning to execution of anext process and the number of specimens processed from start of a lotprocess to end of the lot process; a monitor value estimation unitconfigured to obtain a composite model of the first monitor valuevariation model and the second monitor value variation model andconfigured to calculate a monitor value for a next process based on thecomposite model; a third database that stores a control model indicatinga correlation between a control quantity for controlling a processquantity of the vacuum processing chamber and a quantity of change of amonitor value; and a control quantity calculation unit configured tocalculate a control quantity for the next process which corresponds to adeviation of the monitor value calculated by the monitor valueestimation unit and a target value based on the control model; whereinthe monitor value estimation unit comprises a monitor value variationmodel movement unit configured to move the first monitor value variationmodel or the second monitor value variation model so as to be put on amonitor value for a current process without execution of run-to-runcontrol; wherein the first monitor value variation model is a functionof processed wafers from wet cleaning and at least one long termvariation model coefficient; wherein the second monitor variation modelis a function of the number of processed wafers in a lot and at leastone short-term model coefficient.
 9. A plasma processing apparatus forapplying plasma processing by run-to-run control to specimens that aredisposed in a vacuum processing chamber by using plasma generated in thevacuum processing chamber, comprising: a first database that stores afirst monitor value variation model indicating a correlation between anumber of specimens processed during a period from execution of wetcleaning to execution of a next process and a monitor value of a processquantity obtained when specimens of this number have been processed; asecond database that stores a second monitor value variation modelindicating a correlation between a number of specimens processed duringa period from start of a lot process to end of the lot process and amonitor value of a process quantity obtained when specimens of thisnumber have been processed; a process history management unit thatstores the number of specimens processed from execution of wet cleaningto execution of a next process and the number of specimens processedfrom start of a lot process to end of the lot process; a monitor valueestimation unit configured to obtain a composite model of the firstmonitor value variation model and the second monitor value variationmodel and configured to calculate a monitor value for a next processbased on the composite model; a third database that stores a controlmodel indicating a correlation between a control quantity forcontrolling a process quantity of the vacuum processing chamber and aquantity of change of a monitor value; and a control quantitycalculation unit configured to calculate a control quantity for the nextprocess which corresponds to a deviation of the monitor value calculatedby the monitor value estimation unit and a target value based on thecontrol model; wherein the monitor value estimation unit comprises amonitor value variation model movement unit configured to move thesecond monitor value variation model in parallel so as to be put on amonitor value for a current process without execution of run-to-runcontrol; wherein the first monitor value variation model is a functionof processed wafers from wet cleaning and at least one long termvariation model coefficient; wherein the second monitor variation modelis a function of the number of processed wafers in a lot and at leastone short-term model coefficient.